1. Field of the Invention
The present invention relates to circuit interrupters generally and, more specifically, to those kinds of circuit interrupters having a trip mechanism including an automatic trip assembly for generating a magnetically-induced tripping operation.
2. Description of the Prior Art
Molded case circuit breakers and interrupters are well known in the art as exemplified by U.S. Pat. No. 4,503,408 issued Mar. 5, 1985, to Mrenna et al., and U.S. Pat. No. 5,910,760 issued Jun. 8, 1999 to Malingowski, et al., each of which is assigned to the assignee of the present application and incorporated herein by reference.
Circuit interrupters advantageously provide for automatic circuit interruption (opening of the contacts) when an overcurrent condition is determined to exist. One way of determining whether or not an overcurrent condition exists is to provide a trip mechanism with an automatic trip assembly that reacts to a magnetic field generated by the overcurrent condition. In such circuit interrupters, the reaction to the magnetic field is often in the form of a movement of an armature that, in turn, sets in motion a tripping operation. The movement of the armature normally is either away from or towards a magnetic structure from which the magnetic field emanates, and may be influenced by a member(s) which biases the armature away from the magnetic structure. The magnetic structure is connected to an electrical terminal of the conductor from which electrical current is received.
In the prior art, a head portion of the armature has sometimes been rotatably positioned on pivot supports of the magnetic structure, with a bottom portion of the armature capable of moving either towards or away from the magnetic structure. For this purpose, the head portion of the armature usually has a T-shape that accommodates such a positioning on the pivot supports. Unfortunately, the rotatable disposition of the armature of the prior art does not always provide for smooth movement of the armature. It would be advantageous if an way existed by which to provide a more controlled pivot point for the armature with a low friction bearing surface for providing smoother and more predictable movement of the armature.
The present invention provides a circuit interrupter that meets all of the above-identified needs.
In accordance with the present invention, a circuit interrupter is provided which includes a housing, separable main contacts disposed in the housing, and an operating mechanism disposed in the housing and interconnected with the contacts. Also provided is a trip mechanism disposed in the housing and having an automatic trip assembly that generates a tripping operation to cause the operating mechanism to open the contacts upon a predetermined current threshold. The automatic trip assembly includes an armature and a magnetic yoke having pivot supports. The armature includes a head portion having a first hook-like member and an oppositely facing second hook-like member. The first hook-like member has a first recess, and the second hook-like member has a second recess. The automatic trip assembly includes a pivot pin positioned on the pivot supports and extending through the first recess and the second recess to provide a rotatable disposition of the armature. The assembly also includes a biasing member applying a force to the armature in a direction to normally rotationally displace a bottom portion of the armature away from the magnetic yoke.